Efforts to end the "don't ask, don't tell" law hit another snag Wednesday as Senate Republicans vowed to block any legislation unrelated to government spending or tax cuts, including a defense bill that would end the ban on gays serving openly in the military.

The GOP promise came a day after the Pentagon released a report that pointed a way forward toward ending the ban and as Defense Secretary Robert M. Gates, Joint Chiefs of Staff Chairman Mike Mullen and the report's co-authors prepared to testify Thursday before the Senate Armed Services Committee.

"We've had our heads in this thing for nine-plus months, and it's absolutely fair for the Senate to ask how we got to where we got to," Army Gen. Carter F. Ham, who co-wrote the Pentagon study with Defense Department general counsel Jeh C. Johnson, said this week in an interview.

Many high-ranking military leaders, including some who will testify before the Senate panel on Friday, remain skeptical about or resistant to changing the law - something that Republican opponents are sure to draw upon.

Sen. John McCain (Ariz.), the committee's ranking Republican, was reading the report, a spokeswoman said. He disagrees with how the Pentagon reviews the issue and has called for a new study.

The GOP lawmakers' vow to block non-spending bills "definitely raises the stress level and adds another complication into the mix," said Alexander Nicholson, executive director of Servicemembers United, a group pushing to end the ban. "But I think there is some hope."

Kevin Kelley, a Collins spokesman, said, "Preventing a tax increase and keeping the government operating are her top priorities, but passing a defense authorization bill is also a priority."

Other senators signaled uneasiness Wednesday.

Sen. Joe Manchin (D-W.Va.), who has not declared his position on the matter, said that if the percentage of combat troops opposed to ending the ban was significantly higher, "that raises concerns for me."

About 30 percent of survey respondents cited in the report predicted some degree of negative views or concerns about ending the ban. Opposition and concern were higher among the Marine Corps and other combat specialties.

Sen. Mark Kirk (R-Ill.), a moderate on social issues and a commander in the Navy Reserve, said that he was still reading the report and that he plans to meet next week with Adm. Gary Roughead, the chief of naval operations.